The subject matter disclosed herein relates to spark plugs for internal combustion engines, and more particularly, to electrodes for such spark plugs. More particularly, the subject matter disclosed herein relates to a method of forming the electrodes for such spark plugs.
Conventional spark plugs for internal combustion engines generally include a center electrode and a ground electrode. The center electrode is traditionally mounted within a center bore of an insulator of the spark plug and extends past the insulator at a first end of the spark plug. The ground electrode typically extends from a shell surrounding the insulator near the first end. A spark gap is formed between an end of the center electrode and an end of the ground electrode. Additionally, a noble metal tip is commonly located at the end of one or both of the electrodes facing the spark gap. Traditional spark plug construction frequently includes attaching these noble metal tips directly to the surface of the electrode, often with a joint or weld application.
Modern engine applications expose spark plug electrodes to severe thermal cycling that can create stress on a joint or weld connecting the noble metal tip to the electrode. Over time, such stress can ultimately cause the noble metal tip to detach from the electrode, rendering the spark plug inefficient or inoperable. Spark plugs having a noble metal tip attached to an electrode by a single weld created in a single thermal step are most susceptible to this type of phenomena. A single weld connection created in a single thermal step may result in local stresses at the weld interface between the noble metal tip and the electrode due to the rapid heating and cooling involved in the welding process. These stresses may contribute to premature detachment of the noble metal tip when a spark plug is used in an engine that undergoes thermal cycling.
Accordingly, while existing spark plug electrode manufacturing processes are suitable for their intended purposes, the need for improvement remains, particularly in providing a process of welding a noble metal tip to the electrode that improves the reliability, durability, and the expected life of the spark plug. It is desirable to resolve issues of premature detachment of the noble metal tip by reducing or eliminating the creation of local stress in the weld interface during the welding process of the noble metal tip to the electrode.